EZP-22400: Delegate user context hash generation to FOSHttpCacheBundle

Depends on:
* https://github.com/FriendsOfSymfony/FOSHttpCacheBundle/pull/152
* https://github.com/FriendsOfSymfony/FOSHttpCache/pull/128
Merge pull request #1025 from ezsystems/impl_EZP-22400_FOSHttpCacheBundle

Fix EZP-22400: Use FOSHttpCacheBundle